Position sensing readout

ABSTRACT

Apparatus for determining linear or angular measurements or measurements of positions on a planar or curved surface, which apparatus uses at least one delay element, such as a magnetostrictive element, for example, which is capable of supporting an acoustic wave signal. The one or more delay elements may be in the form of bands, rods, wires, planar or spherical structures, and the like, and can be arranged in various embodiments to provide linear or angular position information for single, dual, and multiaxis geometry. They can be used, for example, to provide single or multispeed resolver operation and three-axis attitude read-out. In preferred embodiments the apparatus uses phase measurement techniques so that high accuracy can be achieved.

This application is a continuation-in-part of Ser. No. 520,742, filed11-4-74, now U.S. Pat. No. 4,035,762.

INTRODUCTION

This invention relates to apparatus for determining a position inlinear, angular, and curvilinear configurations for single and multiaxisgeometry and, more particularly, to apparatus using means, such asmagnetostrictive components, which support travelling acoustic wavesignals by which such angular and distance measurements can beappropriately determined.

BACKGROUND OF THE INVENTION

It is desirable to provide relatively simple means for measuring aposition along a line, either straight or curved, or on a planar orother curvilinear surface, with a high degree of accuracy at areasonable cost. One example of the use of such a measuring device isexemplified by presently known navigation apparatus which use attitudereadout devices for determining the angular orientation of an objectrelative to a set of reference axes for use in inertial navigationsystems, for example. In addition, it is often desirable to know theposition of an object with respect to a reference point along a line oron planar or curved surfaces. Further, it may be desirable to determinethe angular position of a rotating object with respect to a referenceangle.

DESCRIPTION OF THE PRIOR ART

Various devices are presently known for measuring linear or angulardisplacements. For example, various types of resolver devices have beenused in the past for measuring angular displacements (e.g., the angulardisplacements of a rotating shaft). One conventional exemplary type ofresolver (sometimes referred to as a "synchro") generates signals phasemodulated by a shaft angle. Such resolvers make use of the variablecoupling between primary and secondary moving coil windings on a statorand a rotor, in a manner known to the art, in order to perform theangular measurement. Sine and cosine signal components of the angle tobe measured are thereby produced and the angle is appropriatelycalculated as a measurement of tan⁻¹ of the ratio thereof.

Means must be provided for coupling signals between the stator and rotoreither to excite the rotor windings or to receive signals from the rotorwindings. Slip rings or rotary transformers are often used. Usually thewindings are constructed of wire and the complete assembly is likely tooccupy quite a large volume. Construction techniques for minimizingvolume are extremely complicated, and high accuracy is difficult toobtain when volume is restricted.

Another conventional resolver device, often called a "microsyn," alsocan provide phase-modulated signals and offers the advantage oversynchros in that slip rings or rotary transformers are unnecessary.Driver and receiver windings are located on the stator only. The rotorconsists of high-permeability material machined to form salient polesresembling gear teeth, and the angular measurement is effected throughthe variable coupling of magnetic fields from stator windings throughthe rotor structure and back to stator windings. Separate driver andreceiver windings are used on the stator. Since the windings areconstructed of wire, and since the magnetic path requires teethprotruding from the stator and from the rotor, microsyns are difficultto produce in small volumes. Miniature microsyns for inertial componentsare extremely expensive for this reason. Subsequently developed devicescalled the Inductosyn, made and sold by Farrand Controls, Inc. ofValhalla, N.Y., and the wafer resolver, allowed phase-moduled signals tobe obtained from a transducer of much smaller volume. Both theInductosyn and the wafer resolver utilize planar conducting printedpatterns and operate on the principle of variable magnetic couplingbetween patterns on the stator and rotor. With current printed-circuittechnology, very great accuracy can be obtained with extremely smalltransducers of this type. This type of transducer has the furtheradvantage of a very broad signal bandwidth. However, because theInductosyn or wafer resolver has conducting patterns on both the rotorand stator, it requires a separate power or signal channel between therotor and stator. When no mechanical contacts are allowed, a rotarytransformer is usually used, but it occupies a substantial volume andresults in a substantial loss of signal strength. Moreover, undesirableharmonics were generated by the device.

Further development of the Inductosyn device permitted a reduction inthe undesirable harmonics generated therein as described in thefollowing report:

"Optimal Harmonic Reduction In Periodic Switched Wave Forms," James F.Rhodes, C.S. Draper Laboratory Report T-527, January 1970.

A subsequent developed device called the reluctosyn is a printed-patterntransducer combining the advantages of a wafer resolver or Inductosynand microsyn to provide signals that are phase-modulated functions ofmechanical angle without the requirement of a rotary transformer ormechanical contacts.

The stator of the reluctosyn contains planar conducting printed patternsthat are similar to those used in a wafer resolver or in an Inductosyn,with the difference being that the patterns are broken into separateindividual poles which are connected in a separate external circuit.Such a device is described in U.S. Pat. No. 3,641,429 issued to Cox, Jr.et al. on Dec. 24, 1969.

Other devices for providing angular measurements include differentialtransformer transducers, inductance bridge transducers and shorted-turnsignal generators. Differential transformer transducers operate on theprinciple of variable coupling between a primary and two secondarywindings. The fact that the two secondaries are generally connected inseries opposition accounts for the "differential" nature of this device.Both sets of windings are placed within the stator, while ferromagneticmaterial on the rotor is responsible for variations in the primary tosecondary coupling as a function of rotor angle. In the null position,the rotor produces the same coupling from the primary to each secondary.As the rotor moves from the null position, the coupling to one secondaryincreases as that to the other secondary decreases. Both the magnitudeof the output voltage of each secondary and its phase relative to theexcitation voltage are thus related to the extent of this coupling.

In inductance bridge transducers, the motion of the rotor simultaneouslyincreases the inductance in one stator coil and decreases the inductancein the other stator coil. Two arms of a four-arm AC bridge consist ofthis matched pair of stator coils. Assuming that the inductancevariations in each secondary are small to their nominal inductance, theoutput of the bridge is precisely proportional to the inductivedifference between the two secondary coils.

The shorted-turn signal generator comprises four poles, each would withonly one coil. One pair of diametric poles forms the primary(excitation) windings, while the remaining diametric pole pair becomesthe secondary (receiver) windings. A shorted-turn on the rotor is usedto couple signals from one pole pair to the other. The output voltage,appearing across the secondary pole pair, is then a function of therotor's angular displacement.

The above discussed printed pattern devices are subject to furtherdisadvantages in that eddy currents and discontinuities produceundesirable errors in the signal outputs thereof. Moreover, the patternsin such devices must be extremely accurately aligned in order to providethe best operation. Any stretching of the bands on which they areprinted causes the patterns to deform and the linearity of the device islost.

Such printed pattern devices have been used to provide three-axisattitude read-out systems for inertial navigation applications fordetermining angular displacements on a spherical surface, for example.When fabricated for such purposes the devices become even more expensiveand complex due to the whole angle readout calculation which is requiredand to the data processing needed for attitude determination. This addedcomplexity gives rise to reliability problems.

Devices for measuring displacements along a line have been suggested,such devices, for example, being in the form of linear potentiometerswherein a wire wound or conductive plastic resistance element has amovable contact which moves along the line formed thereby to produce achange in resistance proportional to the distance moved. Such devicesmay be formed as straight line devices or as curvilinear devices, inwhich latter case angular measurements can also be made. Linearpotentiometers, however, have relatively low accuracy and problems arisein maintaining the linearity of the signal over the entire resistanceelement. Moreover, the need for a contact between the pickup andresistance element tends to reduce the life thereof, as well as toprevent the use in applications wherein free movement (i.e., "out ofcontact" movement) is required between the pickup component and theresistance element.

Another device suggested for linear position sensing has been disclosedin U.S. Pat. No. 2,947,929 issued Aug. 2, 1960 to J. L. Bowen; thedevice uses a magnetic medium having a magnetically recorded track themagnetization of which is a function (normally a line function) of thedistance along the track. A pair of saturable reactor reading headsmeasure the change in the phase relationships between their outputs asthey move together along the track from a reference point. Theresolution thereof is extremely poor and is limited to no better thanone-quarter wave length of the magnetization pattern.

In the nuclear research area, the use of magnetostrictive elements fordetermining positions on a planar surface, have been suggested in theearly 1960's. For example, one method and structure for locating trackcoordinates in a spark chamber in order to measure position in a planehas been disclosed in the following publications:

1. "A Simple Method Of Increasing Magnetostriction Signals In SparkChambers With Magnetostrictive Readout" -- V. Bohmer et al., NuclearInstruments and Methods 96 (1971), pages 601-603.

2. "Magnetostrictive Readout for `Wire Spark Chambers`" -- V.Perez-Mendex et al., Nuclear, Instruments and Methods 33 (1965), pages141-146.

3. "Construction and Performance of Large Wire Spark Chambers WithMagnetostrictive Read-Out" -- G. Grayer et al., Nuclear Instruments andMethods 99 (1972), pages 579-587.

The coordinates on such a plane are determined by forming a grid patternof perpendicularly intersecting magnetostrictive wire or ribbonelements, the intersections forming a plurality of coordinate points onthe plane. A specific coordinate point can then be determined bydigitizing the time delay from a trigger signal at a reference point tothe arrival of the magnetostrictive pulse at a pick-up coil situated atthe coordinate point to be measured. Such devices are dependent upon thetime measurement of travelling pulsed acoustic signals and, accordingly,may not provide sufficient accuracy for use in many applications. Asimilar form thereof for measuring planar coordinate positions usingmagnetostrictive elements is shown in U.S. Pat. No. 3,648,277, issued toWhetstone et al. on Mar. 7, 1972. Such a device is similar in nature tothe spark chamber devices described above and suffers from the samedisadvantages as to accuracy. Further, such devices cannot besuccessfully used in measuring displacements on curved surfaces as theycannot be effectively adapted for 3-axis attitude readout, or other openor closed curved surface for linear, curvilinear, or angularmeasurements.

Other devices for locating a position along a line have been suggestedutilizing magnetostrictive elements. One such device is made and soldunder the tradename "Temposonic" Linear Displacement Transducers, asmanufactured by Tempo Instruments, Inc., Plainview, N.Y. Such deviceuses the torsional mode of vibration and also the technique of measuringthe time interval for such torsional mode sonic pulse to travel along amagnetostrictive wire in order to determine the distance between twopoints along the wire. Measurements of time delays by the use oftorsional pulsed sonic signals provide insufficient accuracy for manyapplications. Moreover, such devices are used only for lineardisplacements and, accordingly, have never been adapted to yielddisplacement information with respect to a planar or other curvilinearsurface or for use in measuring angular displacements. Moreover, theycannot be effectively adapted to 3 axis attitude readouts.

SUMMARY OF THE INVENTION

The invention overcomes the disadvantages of the above discussed priorart devices and provides for linear or angular measurements ormeasurements of positions on a planar or curved surface, as for 3 axisattitude read-out determination, for example. The embodiments of theinvention generally can be manufactured at substantially less cost thanthe more complicated of the above-described devices since littleprecision work is required and the electronic circuitry required for usetherewith is considerably simplified. Despite the simplicity and lowercosts thereof, the invention can provide a high degree of accuracy inproducing displacement information without the introduction of errorsdue to problems of eddy currents, discontinuities, misregistration, andstretching.

Further, the invention is inherently linear due to the wave propagationphenomena and theoretically has an infinite resolution. It is moreaccurate than the printed pattern devices because the positionmeasurement is dependent on the phase of one signal and not on theamplitude and phase of two signals.

Another advantage of the invention is its variable resolver multispeedcapabilities. The resolver speed of this device is controlled by thefrequency of the driving signal and is not fixed, as in the printedpattern devices.

Moreover, because of the reduction in manufacturing complexity, the useof relatively simple transducer elements, and the use of relativelysimple electronic circuitry in association therewith, a reduction inpower consumption can be achieved. Improved accuracy can be achievedbecause of better linearity particularly where, in comparison withprinted pattern systems, the systems of the invention can be arranged toprovide direct angular readouts, for example, or incremental angularreadouts. Overall, the invention provides improved reliability andsmaller volume requirements so that it can be utilized in applicationswhere spatial requirements are limited. Moreover, there is no need togenerate computer programs which are required to draw the printedpatterns during the manufacture of the prior art system so that savingsin the time and costs thereof are achieved.

In accordance with the invention, a delay element capable of supportinga travelling acoustic wave, such element being in the form of amagnetostrictive element, for example, is used to determine an angularor linear displacement or a displacement along a planar or curvedsurface. The displacement measurement generally depends upon ameasurement of the phase of a continuing wave travelling acoustic signalin the delay element relative to a reference phase. The magnetostrictivedelay element may be in the form of one or more bands, rods, single wireor multi-wire structures, etc., formed in straight or curved lineconfiguration. Such delay elements may be formed in other than bands,rods, wires, etc., such as in planar or curved shell-type structures, asdescribed in more detail below. Further, the bands, rods, shells, etc.may be homogeneous magnetostrictive materials or may includenon-magnetostrictive portions as, for example in configurations having anon-magnetostrictive core plated with a material exhibitingmagnetostrictive properties or a configuration using serially coupledsegments of different materials. The use of phase measurements in somepreferred embodiments of the invention as opposed to the time delaymeasurements used in other certain prior art devices greatly increasesthe accuracy which is achievable.

In summary, the invention uses sonic wave supporting delay elementswhich can be arranged in various embodiments to provide for linearposition information or angular position information for single, dualand multiaxis geometry. In a particular arrangement the invention canprovide resolver operation as a superfine, highly accurate transducerthat generates signals phase-modulated by a shaft angle or by linearmotion. Further, such resolver operation can provide variable speedoperations. Further, the invention can provide position information withrespect to a plane or a curved surface, and, in particular, for example,as a 3-axis attitude readout apparatus for measuring spatialorientation. Further, the invention can be used in a dual delay elementconfiguration to provide planar position sensing, wherein either delayelement can be used as an input device to provide an input signal or asan output device to pick up the output signal. Moreover, the device canbe used in a bandless form to provide planar or spherical surfaceposition sensing. Further, the invention can use transverse wavespropagated in the delay element to improve the resolution of theposition readout. Moreover, the invention can provide for sine andcosine output signals using a standing wave created in the delayelement.

DESCRIPTION OF THE INVENTION

The invention can be described in more detail with the assistance of theaccompanying drawings wherein

FIG. 1 shows an effective block diagram of one embodiment of theinvention for providing a single axis position determination;

FIG. 2 depicts wave forms helpful in understanding the operation of theembodiment of FIG. 1;

FIG. 3 depicts a plurality of different embodiments of the transducerelements of the invention;

FIGS. 4 and 5 depict alternative embodiments of the invention of FIG. 1for use in providing resolver operation;

FIG. 6 depicts an embodiment of the invention for determining theposition on a planar surface;

FIG. 7 depicts an embodiment of the invention for determining an angularposition about a single axis;

FIG. 8 depicts an embodiment of the invention which is a modification ofthe embodiment of FIG. 7;

FIG. 9 depicts an embodiment of the invention for determining angularpositions in a two-axis system;

FIG. 10 depicts an embodiment of the invention for providing athree-axis attitude readout system;

FIG. 11 depicts a modification of the embodiment shown in FIG. 6;

FIGS. 12-14 depict an embodiment of the invention for providing aprecision pendulum system for determining a reference position relativeto a vertical direction;

FIGS. 15, 16 and 16A depict an alternative embodiment of the inventionfor determining a position on a plane surface;

FIGS. 17 and 17A depict alternative embodiments of the invention fordetermining a position on a spherical surface;

FIG. 18 depicts an embodiment of the invention which illustrates meansfor compensating for operation of the invention with temperaturechanges;

FIGS. 19, 20 and 21 depict alternative embodiments of the invention forproviding resolver operation;

FIG. 22 depicts a further embodiment of the invention specifically usingtransverse waves therein;

FIG. 23 depicts a still further embodiment of the invention usingtransverse and longitudinal waves;

FIG. 24 depicts a still further embodiment of the invention using atransverse wave together with a plurality of receiver transducers;

FIG. 25 depicts an alternative embodiment of the invention forgenerating sine and cosine signals; and

FIG. 26 depicts a further alternative embodiment of the invention forgenerating sine and cosine signals.

As shown in FIG. 1 the invention can be utilized to determine a linearposition along a single axis. As depicted therein, the inventioncomprises a magnetically coupled delay line element 10 which, in apreferred embodiment, can be a rod of ferromagnetic material havingmagnetostrictive characteristics. Alternatively, the element 10 may be asingle wire, or a bundle of wires or any other magnetically coupledelement which can support a travelling acoustic wave. The element 10 ismounted at either end in a termination block 11 which is fabricated soas to provide a means for absorbing the acoustic wave which impingesthereon. Such material may be clamped rubber, other similar elastomermaterial, or lead for such purpose.

An input or transmitting transducer 12 is arranged to be appropriatelycoupled at a selected reference point or reference region along themagnetostrictive element 10, corresponding to the reference line 12A,for example, for providing an excitation thereof to produce a travellingacoustic wave on the element, as explained in more detail below. Areceiving transducer 13 is located at a position, corresponding toreference line 13A, for example, to be determined with respect to thereference position of the input transmitting transducer 12. Thus, asshown therein, it is desirable to determine the distance X₀ between theinput and output transducers 12 and 13.

In the particular embodiment of FIG. 1, the transmitting transducer 12is supplied with a continuous wave electrical signal for exciting acontinuous travelling wave acoustic signal. Such electrical signal isobtained through an appropriate continuous wave signal source 14 whichis fed to the transmitting transducer via a variable gain amplifier 15,as explained below. The output of signal source 14 is also fed to oneinput of an appropriate phase detector 16 which may be of a conventionaltype for determining the phase difference between a pair of inputsignals. The other input of phase detector 16 is obtained from theelectrical output of receiving transducer 13 via a suitable amplifier 17so that the input signals 22 and 23 of phase detector 16 are ofcomparable levels. The output of variable gain amplifier 15 is fed tothe "Start" input of a time delay counter circuit 18 via thresholddetector circuitry 19. The output of amplifier 17 is fed to the "stop"input of a time delay counter 18 via a threshold circuit 20. The latteroutput signal is also fed to a threshold detector circuit 21 whichdetects a decrease in amplitude thereof to provide a reset signal forthe reset input of time delay counter 18. The operation of the systemshown in FIG. 1 can be summarized as follows.

The variable gain amplifier 15 has a gain characteristic A(t) as shownby the dashed line envelope 25 of wave form 24 in FIG. 2 wherein thegain is increased in a step function at time t₁ and decreased in a stepfunction at time t₂. The acoustic wave which is thus excited for travelalong the magnetostrictive element 10 increases its amplitude sharply attime t₁ and decreases its amplitude sharply at time t₂. The receivedwave signal is appropriately amplified following its pickup by receivertransducer 13 and is shown by wave form 26 in FIG. 2A. The increasedthreshold level of the received wave is not picked up at the receivertransducer until a time t₃ after a time interval τ, shown in FIG. 2A,which represents the time of travel of the input wave alongmagnetostrictive element 10. Such time of travel is utilized todetermine the "coarse" position readout of the receiver transducer 13.

Thus, threshold detector 19 provides an output signal when the thresholdlevel at the output of variable gain amplifier 15 increases (at t₁ ) soas to start the count of time delay counter 18. When the threshold levelincrease is detected at time t₃ (where t₃ - t₁ = τ) by thresholddetector 20 in the output signal from amplifier 17, a "stop" signal issupplied from detector 20 to stop the counter 18. The number of integralcycles so counted then determines coarsely the approximate distanceX_(O) which is directly measured by the time interval τ and a knowledgeof the speed of travel of the acoustic wave within the magnetostrictiveelement 10. In order to provide a "fine" readout of the distance, ameasurement of the phase shift between the transmitted signal and thereceived signal is required, such phase shift being depicted in FIG. 2as phase shift φ which is the same in any comparable cycle of wave formsignals 24 and 26.

The counter 18 can be reset by detecting the time t₄ at which thethreshold level of the received signal decreases from its higher to itslower level, as shown in FIG. 2A, at which point the output of thresholddetector 21 provides a reset pulse signal so that the counter can bereset to zero so as to be able to resume its counting for the nextmeasurement.

The position of receiving transducer 13 is thereby determined extremelyaccurately by the determination of the phase shift of the acoustic wavesignal as it travels down the magnetostrictive delay line.

The receiving transducer can assume a variety of different exemplaryforms (A) through (I) as shown in FIG. 3. In form (A), the receivingtransducer is a coil 13A which is concentrically wound aroundmagnetostrictive element 10. Form (B) uses an N-turn loop 13B (only oneturn is shown for simplicity) which is placed adjacent the delay line.Form (C) shows a plurality of coils 25 for transducer 13C, all of suchcoils being spaced from each other by a distance "d" which is equal toone wave length of the acoustic wave signal which travels along themagnetostrictive delay line. Form (D) shows a plurality of loops 26 fortransducer 13D, such loops being separated by a distance "d" equal toone wave length as in (C) above.

Form (E) is a single conductor 27 positioned adjacent the delay line asshown by transducer 13E, while form (F) is a conductive element 28 inthe form of a square wave pattern placed adjacent a selected length ofthe delay line 10, the period of the square wave being substantiallyequal to the period of the acoustic wave signal as shown by transducer13F. Form (G) is a plurality of circular loops 28 forming a conductivepath as shown by transducer 13G, such loops being wound aroundmagnetostrictive element 10 in a periodic pattern having a periodsubstantially equal to the wave length of the acoustic wave. Form (H) isa conductive element in the form of a trapezoidal pattern 29 as shown bytransducer 13H, the period, as above, being substantially equal to theperiod of the acoustic wave.

In the forms generally shown as (F), (G) and (H) in FIG. 3 the receivingtransducer pattern may be used to determine either the overall change inthe position of the receiver transducer from a reference point, or theincremental change in such position over a single period of the receivertransducer pattern, that is, the incremental changes thereof as thereceiver transducer moves relative to the delay line. In the latterinstance, the receiver transducer motion is limited to an amount whichis less than one wave length, in which case the input signal need not bemodulated in any way and a measurement of the phase difference betweenthe input acoustic travelling wave and the received travelling waveacross the end points of the receiver transducer pattern provides adirect measurement of the incremental position change of the receivertransducer relative to the delay line. In the former instance, where thereceiver transducer is moved by an amount which is greater than onewavelength, it is necessary to provide a coarse measurement as discussedabove. One way to do so would be to use an appropriate counter to counteach time one wave length of the receiver pattern has been traversed.The "fine" measurement is then obtained by a measurement of the phasedifference of the input wave and the received wave across the end pointsof the receiver transducers of (F), (G), or (H).

Although the transducer patterns (F), (G) and (H) are referred to asreceiver transducers, they can also be used as driver transducers byexcitation thereof by a signal across their end points, in which casethe transducer 12 of FIG. 1, for example, is used as a receivertransducer. Such a configuration tends to provide a cleaner signal and abetter signal to noise (S/N) ratio.

Thus, a continuous measurement of the change in position of the receivertransducer may be obtained or, if desired, the absolute position of astationary receiver transducer relative to a reference position can beobtained.

Form (I) is a conductive loop 30 having a configuration such that twopoints thereof are effectively positioned adjacent the magnetostrictiveelement, as shown by transducer 13H, which is adjacent delay line 10 atthe points 31 and 32. Other forms of the receiving transducer may alsooccur to those in the art within the spirit and scope of the invention.

Further, the transmitting transducer may also assume one of the formsshown in FIG. 3. While such transducers are shown as being magneticallycoupled to the magnetostrictive element, they may alternatively beformed in any other manner which would provide for the excitation of anacoustic wave at the transmitting end and a pickup of the acoustic waveat the receiving end. Such forms may include mechanically coupledelements driven by electrical signals such as piezoelectric crystals,for example, or driven by mechanical means, such as vibrators, etc., andindeed any other transducer elements known to those in the art whichwill produce an acoustic wave in element 10 or which will pick up anacoustic wave therefrom can be used.

While the embodiment of FIG. 1 has been described in connection with itsuse in measuring a position along a line, such device can also be usedin a manner equivalent to previously known electrical resolvers. Suchdevices are used to measure angular change, i.e., the total number ofrevolutions through 360 electrical degrees and partial revolutionsthereof that may have occurred. The output of receiver transducer 13provides a direct readout of such an angular measurement when comparedwith a zero reference angle at the input transducer 10.

One specific embodiment of the invention for use as a resolver canutilize a receiver transducer element in the form of a wave patternsimilar to those discussed with reference to forms (F), (G) and (H), forexample, of FIG. 3. One such embodiment, which can be referred to ashaving a co-planar resolver configuration, is depicted in FIGS. 19 and20. A first input band 135 of magnetostrictive material is formed in acircular configuration substantially in a plane 136 on the outer surfaceof a rotatable cylinder 137. A second receiver band 138, co-planar withinput band 135, is formed on the inner surface of a concentriccylindrical member 139. The receiver band 138 is in the form of aperiodic wave pattern, such as a square wave pattern, for example, whichextends substantially completely around the input band 135, the outercylindrical member 139 also forming a housing for the device. The inputband 135 has an input transducer element 140 which can be excited togenerate a travelling acoustic wave signal along the inner band 135. Theends of the receiver transducer band pattern 138 are available at pointsA and B. The input cylinder 137 is mounted, for example, on a shaft 141so as to be rotatably movable relative to the receiver band, the latterbeing held stationary.

Thus, the angular displacement of the input band relative to thereceiver band can be determined to produce a resolver operation. Inaccordance therewith, a travelling acoustic signal is generated fortravel along the input band by excitation of the input transducerelement 140 and the distance of travel thereof with respect to a pointon the receiver band pattern can then be determined. The "coarse"distance from a reference point can be determined, for example, bycounting the number of wavelengths of the receiver transducer bandpattern 138 which are traversed by the travelling acoustic wave, via anappropriate counting means (not shown) in a manner which would be wellknown to those in the art. The "fine" distance, i.e., the distancewithin one wavelength of the receiver pattern, can be determinedaccurately by comparing the phase of the received signal picked up bythe receiver transducer pattern relative to the phase of the inputsignal generated at input transducer element 140 as a reference.Accordingly, the desired resolver measurement of the angular position ofthe input band relative to the receiver band can be determined to a highdegree of accuracy.

An alternative form of the co-planar device of FIGS. 19 and 20 is shownin FIG. 21 which can be referred to as a disk type resolverconfiguration. As seen therein, a magnetostrictive input band 145 isplaced on a flat side of a first disk 146 which is mounted adjacent asecond disk 148 having a receiver transducer pattern 147 placed thereon.The disks are mounted so that the position of the input band 145 on thelower side of disk 146 is opposite to and aligned with the position ofreceiver pattern 147. The ends of input band 145 are brought out throughan opening in disk 146 to the upper side thereof where they areappropriately mounted. An input transducer 149 is utilized to generate atravelling acoustic wave signal along band 145 as discussed above. Theends of receiver transducer wave pattern 147 are available at points Aand B at the opposite of disk 148.

The disks are mounted so as to be relatively movable in rotation withrespect to each other. Thus, disk 148 may be held stationary, forexample, and disk 146 mounted to be rotated about axis 150. The "coarse"and "fine" measurement of the angular position of the rotating disk inthereupon measured in a manner such as discussed above with reference toFIGS. 19 and 20.

Although the configurations of FIGS. 19-21 are described specifically asbeing mounted so that the input band rotates relative to a stationaryreceiver band, it is clear that the input band may be held stationaryand the receiver rotated or that both bands be mounted so as to rotaterelative to each other. In any case a measurement of the angularposition of one relative to the other can be made with a high degree ofaccuracy.

In some applications the device of FIG. 1 may be used to replacepresently known resolvers the output signals of which are not directangular measurements but rather represent the "sine" and "cosine"components thereof, appropriate calculations being made therewith todetermine the angle which is being measured. Thus, such outputs mayrepresent, for example, "sin θ" and "cos θ," the angle θ then beingcalculated as tan⁻¹ (sin θ)/(cos θ). In such applications it may bedesirable to retain the presently used calculation system whileinstituting the device of FIG. 1 for the previously used resolver deviceonly, in which case the device of FIG. 1 which provides a direct anglemeasurement must be modified to provide the sine and cosine componentsthereof instead.

Such a device is shown in FIG. 4 wherein the input transducer systemcoupled to delay line element 95 is in the form of two input transducers96 and 97 which are located at a distance "d" from each other. The inputtransducers are alternately excited with a continuous wave signal from amultiplexed signal source 98. The distance "d" is made equal to (λ/4 +N2π), where λ is the wavelength of the excitation signal and N can be 0,1, 2, 3, . . . ,etc. A pair of acoustic continuous wave signals arethereby successively generated along delay line 95, such waves differingin phase by 90° (or λ/4). The acoustic waves are successively picked upat receiver transducer 99, the successive outputs of which are fed to aphase sensitive detector 100, which successively provides outputsignals, the amplitudes of which vary as a function of the phase of theinput signals thereto. Accordingly, "sine" wave and "cosine" wavecomponents are successively present at the outputs of phase sensitivedetector 100, which components are appropriately used, as in presentlyknown electrical resolvers, to provide a suitable angle calculation asshown.

The embodiment of FIG. 4 can be modified to provide the desired outputcomponents in a manner shown in FIG. 5 in which a signal inputtransducer 105 is coupled to a delay line element 106. An inputcontinuous wave signal is applied thereto from a source 107 whereupon anacoustic continuous wave signal is generated along delay line 106. Apair of output transducers 108 are coupled to delay line element 106 andare positioned at a distance "d" apart from each other. As above, thedistance "d" is equal to (λ/4 + N2π). The outputs of transducers 108 arefed to a suitable multiplexer 109, the output of which is fed to a phasesensitive detector 109A, the outputs of which represent the desired sineand cosine components, respectively, so that the appropriate anglecalculation can be made, as above.

Unlike prior art resolver devices in which the frequency of the wavepattern utilized therein is fixed and cannot be dynamically changed, theresolver configurations of the invention permit the design of a"variable speed" resolver, i.e., one in which the frequency of theexcitation wave can be varied. Such variation can be accomplished byvarying the frequency of the input wave from CW signal sources 98 and107, for example.

A determination of a position in an X-Y, or two-axis, system can be madewith the use of a structure as shown in FIG. 6. A pair of delay lineelements such as magnetostrictive rods 10 and 30 are positioned at aknown angle with respect to each other (one such known angle can be aright angle as shown in the specific embodiment depicted) and aremovable relative to each other along the X and Y axes in such a mannerthat the values of X and Y as shown therein vary. Each of themagnetostrictive elements is mounted in a pair of terminal blocks at itsend as shown by terminal blocks 11 and 31 in the manner discussed abovewith reference to FIG. 1. Each delay line has an input transmittingtransducer such as transducers 12 and 32, respectively, as shown in FIG.6. In each case the magnetostrictive element itself acts as a receivertransducer for determining the X and Y positions.

Thus, in order to determine the X position, the input transducer 12 isexcited with an appropriate continuous wave signal to provide anacoustic wave signal along element 10, as discussed above with referenceto FIG. 1. The magnetostrictive element 30 effectively acts as areceiver transducer and provides a received signal across points C and Din the same manner discussed with reference to the receiver transducerof FIG. 1, element 30 acting in a manner analogous to the single wireembodiment of FIG. 3(E). Appropriate circuitry as discussed above canthereby be utilized to determine the position of magnetostrictiveelement 30 along the axis represented by magnetostrictive element 10and, hence, the distance X as shown in FIG. 6.

In a similar manner, in order to determine the Y position, inputtransmitting transducer 32 is excited by an appropriate continuous wavesignal for generating an acoustic wave along delay line 30. In this caseelement 10 acts as a receiver transducer to provide a received signalacross points A and B which can be utilized with appropriate circuitry,as discussed above, for determining the distance from input transducer32 to magnetostrictive element 10 and, hence, the distance Y as shown inFIG. 6. The principles of operation discussed with reference to thetwo-dimensional position determination can be extended to three or moredimensions if required.

The configuration of FIG. 6 may be operated in another manner to achievethe same results. Thus, the delay elements 10 and 30 may be used asinput transducers and the transducers 12 and 32 may be used as receivedtransducers. Accordingly, in order to obtain a measurement of "X" thedelay line 30 may be excited by applying an appropriate input signalacross its ends C and D, the excitation thereof providing an acoustictravelling wave along delay line 10 which is thereupon received bytransducer 12, the received signal being then utilized with appropriatecircuitry, as discussed above, to determine the distance from delay line30 to transducer 12. Similarly the distance "Y" may be measured byexcitation of delay line 10 across its ends A and B, which generates anacoustic travelling wave along delay line 30 which is received bytransducer 32.

Alternatively, the configuration of FIG. 6 can also be operated so tahtthe input or driver elements for such measurements are always associatedwith the same delay element. For example, the measurement of X may bemade by excitation of transducer 12 to generate an acoustic travellingwave along delay element 10 which is received across the ends C and D ofdelay element 30. The measurement of Y may be made by excitation ofdelay element 10 across its ends A and B to generate an acoustictravelling wave along delay element 30 which is received by transducer32. Conversely, delay element 30 and its transducer may be used asdriver elements with delay element 10 and its transducer 12 being usedas receiver elements in the same manner.

The principles of the invention can also be utilized to make adetermination of angular position as shown in FIG. 7. For such purpose amagnetically coupled delay line such as a rod or band ofmagnetostrictive material 40 can be formed in a circular arc, such as asemicircle as shown and held at termination blocks 41. An inputtransducer 42 is fixedly located along a reference line 45 and areceiver transducer 43 is pivotally mounted at a pivot point 44 so as tobe rotatably moved from a 0° reference angle along line 45 to a finalreference angle at the other end of said line, shown as 180° referenceangle in FIG. 7. Accordingly, a continuous wave signal applied totransducer 42 will excite an acoustic wave in element 40 which wave willtravel along element 40 and be received by receiver transducer element43 at the angle to be determined with reference to the 0° referenceangle. The distance travelled along element 40 can be readily calculatedin angular terms so that an accurate measurement of the angle can bemade. The measurement may alternatively be made by using transducer 43as the input transducer and transducer 42 as the output transducer.

The principles of FIG. 7 can be extended to provide angular measurementseffectively over a 360° range in accordance with the configuration shownin FIG. 8, wherein a delay line magnetostrictive element 46 is fashionedin the form of a substantially complete circle and the receivertransducer 48 is pivotally mounted at the center 49 thereof. The ends ofdelay line 46 are appropriately mounted in termination blocks 47. Aninput transmitting transducer 50 is effectively mounted along a 0°reference line 51 so that the angle β with reference thereto can bemeasured by the reception at transducer 48 of an acoustic wave which isgenerated so as to travel from input transducer 50 alongmagnetostrictive element 46. Interchanging the functions of transducers48 and 50 can be provided for as discussed above with reference to FIG.7.

The concepts of FIG. 8 can be extended to a two-axis angular positionmeasuring system in the manner shown in FIG. 9 wherein delay lineelements 52 and 53 are arranged at a known angle with respect to eachother (arranged to provide mutual orthogonality in the specificembodiment of FIG. 9) to provide for angular measurements φ and θ, asshown. One delay line element can act as a receiver for the other delayline element in a manner analogous to the planar position measuringdevice discussed with reference to FIG. 6. Thus, in order to measure theangle φ an input transducer 54 is excited to produce an acoustic wavewhich travels along delay line element 52. The orientation of delay lineelement 53 with reference to a 0° reference line 55 in the plane ofelement 52 determines the angle φ and element 53 acts as a receivertransducer for producing a received continuous wave signal across pointsA and B thereof. In a similar manner the angle θ can be measured byexciting an acoustic wave via input transducer 56 for travel alongelement 53, in which case delay line element 52 acts as a receivertransducer and its orientation with respect to a 0° reference line 59determines the angle θ in accordance with the received wave producedacross points C and D.

In a manner similar to that discussed above with reference to FIG. 6,the configuration of FIG. 9 may be operated so as to apply an inputexcitation signal across delay line 53 so as to generate an acoustictravelling wave along delay line 52 to be received at transducer 54 inorder to measure the angle φ and to apply an input excitation signalacross delay line 52 so as to generate an acoustic travelling wave alongdelay line 53 to be received at transducer 56 in order to measure theangle θ.

Further, as discussed above with reference to FIG. 6, it it is desiredthat the driver transducers be associated with one of the delayelements, transducer 54 and delay line 52 may be used as input elementsand delay line 53 and transducer 55, respectively, used as receiverelements. Alternatively, the functions of such elements may beinterchanged as discussed above.

Use of the principle of the invention as discussed above with referenceto the two-axis system of FIG. 9, for example, can be made in extendingthe principles to provide a three-axis attitude readout system as shownin FIG. 10. The configuration thereof is based on the "floated ball"concept wherein, as is well-known in the art, an inner sphericalplatform 60 is encased within a spherical shell (not shown). The sphere60 reposes or floats, in a liquid, within the shell. The inner sphericalplatform is usually stabilized to maintain a substantially fixedposition with respect to designated reference coordinates, while theouter spherical shell is permitted to move freely relative to the innersphere.

In accordance with the principles of the invention, three separatemagnetostrictive element driver bands 61, 62 and 63 are orthogonallymounted on the surface of spherical platform 60 while the concentricspherical shell has a receiver band 64 located on its inner surface. Themagnetostrictive element bands 61, 62 and 63 are mounted in terminalblocks (for simplicity, not shown) within sphere 60 in a manner similarto that shown with respect to FIG. 9, for example, and each has atransducer (not specifically shown) appropriately mounted thereon at oneend thereof within the sphere in substantially the same manner. Thereceiver band 64 is mounted in terminal blocks (not shown) external tothe shell and has a transducer appropriately mounted at one end thereof.Receiver band 64 is used to determine the angular relationships betweenitself and each of the driver bands in the manner discussed withreference to FIG. 9, wherein its two angular relationship with each ofthe driver bands can be determined separately and consecutively so thatthe angular position thereof with reference to each of the driver bandson the spherical surface 60 can be suitably calculated.

Thus, in order to make each of such angular measurements, the techniquediscussed above with respect to FIG. 9 can be used. For example,excitation of the transducer on driver band 61 and pick up by receiverband 64 provides a first angular measurement, while excitation of thetransducer on receiver band 64 and pick up by driver band 61 providesthe second angular measurement, the same method being used with respectto each of the driver bands relative to the receiver band.

While, in general, measurements of the angular relationships betweenonly two driver bands with respect to the receiver band (and, hence, theouter shell on which it is mounted) are required to completely definethe angular position of the outer shell relative to the inner stablespherical platform 60, such measurements are not possible when thereceiver band is oriented so as to be substantially parallel to, andcontiguous with, a particular driver band. In such a case, measurementsof the angular relationships between the other, non-parallel driverbands can be made. Accordingly, three driver bands are used to provideinformation concerning all relative orientations of the outer shell andinner sphere.

Although the above technique of exciting the driver band and thereceiver band transducers and of picking up the travelling wave signalwith the corresponding band can be used, the specific structure requiredfor applying the excitation signals and for obtaining the receivedsignals and supplying them to an appropriate means for computing theangles involved may be relatively complicated. The overall structure maybe simplified by utilizing the driver bands only for excitation by theinput signals and by utilizing the receiver band only for picking up thereceived signals and for supplying them to a suitable angle computer. Inthis way, all of the driver excitation components can be mountedtogether within the sphere and all of the receiver and computationcomponents can be mounted together externally to the outer shell.

In such a case, measurements of the angles involved can be made, first,by exciting the transducer of a particular driver band to produce anacoustic travelling wave along the driver band which is then picked upby the receiver band to provide a first received signal across thereceiver band and, second, by exciting the driver band itself byapplying a signal across its ends to produce an acoustic travelling wavealong the receiver band which is then picked up by the transducer of thereceiver band to provide a second received signal at the lattertransducer.

Although in the above configuration, the magnetostructive elements usedin each case are in the form of single rods, wires, or bundles of wires,etc., it is often desirable to improve the signal to noise ratio whensuch apparatus is used in relatively noisy environments. Suchimprovement can be accomplished in the manner shown with reference toFIG. 11. Although the discussion relates to the configuration of FIG. 6,the same principle can be used in the other configurations discussedabove. In FIG. 11, a first pair of parallel mounted magnetostrictiveelements 70 and 71 are mounted so as to have a known angularrelationship with respect to a second pair of parallel mountedmagnetostrictive elements 72 and 73. In the embodiment depicted, theelements are mounted orthogonally, although in a general case theangular relationship can be other than orthogonal. Each element ismounted at its ends in termination blocks 74 and each element has aninput transducer 75 associated therewith. The elements 70 and 71 areelectrically connected via an appropriate conductor 76 and when used asa receiver transducer can provide an output signal across points A andB. Similarly, elements 72 and 73 are electrically connected viaconductor 77 and when used as a receiver transducer provided an outputsignal across points C and D.

In order to determine the position X, effectively representing thedistance from input transducers 75 on elements 70 and 71 to the centerpoint 78 (representing the average distance of elements 72 and 73therefrom), the input transducers of elements 70 and 71 are excitedsimultaneously with a continuous wave signal so as to producesimultaneous acoustic waves along magnetostrictive elements 70 and 71,which waves are simultaneously received by elements 72 and 73 to producea received continuous wave signal across points C and D, which receivedsignal can be used as discussed above to provide an accurate measurementof the distance X.

A similar measurement can be performed for determining the distance Y byexcitation of the input transducers 75 of elements 72 and 73 andreception by elements 70 and 71 acting as receiver transducers toproduce a continuous wave received signal across points A and B.

In accordance with the configuration of FIG. 11, the use of a pair ofmagnetostrictive elements in each case provides increased signalstrengths so that the overall signal-to-noise ratio is improved and theapparatus becomes extremely useful in environments subject to noiseproblems.

As discussed above, the functions of the transducers and delay lines canbe interchanged and the driver functions may be associated with one pairof delay line elements and the receiver functions associated with theother pair thereof.

The principles of the invention can be utilized to provide a referenceto a vertical direction through the use of an appropriate precisionpendulum configuration, as shown in FIGS. 12 - 14. As depicted therein,an outer cylinder 80 is used to house a pendulum 85 which is movablerelative to cylinder 80 by being pivotally mounted along axis 86. In agravitational field, the pendulum 85 assumes a vertical orientationalong the direction 90 as shown.

A receiving transducer is formed on the inner surface of cylinder 80 inthe form of a conductive transducer element 81 in a square-wave looppattern which is depicted in FIG. 13 and is shown in linear form in FIG.14. The receiving transducer pattern extends completely around andadjacent the inner surface of cylinder 80, its ends being made availableat points A and B, as seen in FIG. 12.

Pendulum element 85 is in the form of a substantially solid halfcylinder having an outer peripheral surface, the configuration of whichcorresponds to the inner surface of cylinder 80. A magnetostrictiveelement 82 is positioned around the outer surface of pendulum 85 asshown in FIG. 12 and is mounted thereon in termination blocks 83 at itsinner ends. An input transmitting transducer 84 is mounted as shown inFIG. 12 at one end of magnetostrictive delay line element 82. Outercylinder 80 is fixedly attached to a movable component whose verticalaxis it is desired to stabilize, such as a ship, for example, in anoceanographic application. The purpose of the pendulum structure is todetermine when the component (and, hence, the cylinder 80) is in aposition off the vertical 90 and to measure the angular offsettherefrom, such measurement providing information for use in anappropriate servomechanism system to move the component back to itsvertical position so that stabilization thereof occurs. For such purposeit is desirable to determine the angular displacement of cylinder 80with reference to the vertical direction 90 of the pendulum 85. Suchangular direction can be readily determined by exciting magnetostrictiveelement 82 with a travelling wave and determining the distance of travelalong the receiving transducer loop pattern and accurately determiningthe phase shift with reference to the specific pattern cycle so that ameasurement of the angle can be readily determined, as discussed above.A direct measurement of the position of the outer cylinder withreference to the vertical direction can then be made so that appropriatecorrection or other use thereof can be made.

Although the configuration shown in FIG. 12 utilizes a magnetostrictiveelement on the pendulum and a receiver transducer element on thecylinder, such elements can be interchanged so that the magnetostrictiveelement can be mounted on the inner surface of the cylinder and thereceiver transducer element pattern placed on the outer peripheralsurface of the pendulum structure.

Such an apparatus can be useful in providing an accurate pendulum foruse in numerous aerospace, oceanographic and industrial applicationswherein direct electrical reference to a vertical direction is needed.Such devices may be used to control, or record, pitch and roll angles onseagoing vessels or other marine devices such as torpedoes, or tomaintain a remote component in a level orientation with reference to avertical direction, or to measure angles on industrial equipment so asnot to exceed safe limits or maximum allowable angles of operation, orto provide an attitude reference to determine a specific reference froma known angle.

Although the above embodiments of the invention generally disclose theuse of a ferromagnetic material in a delay line configuration as in theform of rods, wires, bands, and the like, the invention is notnecessarily limited to the use of only such forms thereof. Thus, thedelay element may be in the form of a planar element, or plate, forexample, to provide a determination of a position on a planar surface.

In the specific configuration shown in FIG. 15, the delay element is aplate, or sheet, 110 of ferromagnetic material. Three input transducerelements 111, 112 and 113, shown in more detail in FIGS. 16 and 16A, arepositioned at points, or regions, A, B and C, respectively, on thesurface of plate 110. A receiver transducer 114 in the form of a coil,for example, is located adjacent a position to be determined on thesurface of plate 110, as shown.

Each of the input transducer elements may be formed, for example, asshown in FIGS. 16 and 16A wherein a cylindrical ferrite core 115 has anouter shell 116 closed at one end thereof and an inner core leg 117 onwhich is wound a coil 118, as shown. The open end of shell 116 of eachtransducer element is placed into contact with the surface of plate 110and the coils thereof are appropriately and successively excited with asuitable electrical signal from a suitable multiplexed signal source andsuch coils thereupon generate omnidirectional acoustic wave signals inplate 110 emanating from each of the regions at which each of the inputtransducers is placed. The acoustic wave signals from each of the inputtransducers are suitably damped by a damping material 119, such asclamped rubber, which is used around the edges of plate 110 so as toprovide a termination strip which prevents reflection of the acousticwaves at the discontinuities formed by such edges. Such acoustic wavesignals are picked up by receiver transducer 114 to provide signalsrepresenting the distances from each input transducer to the receivertransducer. An appropriate calculation can be made at a suitablecomputation means from the information provided by such signals and frominformation of the known positions of the input transducers on plate 110in accordance with known "triangulation" techniques to determine theposition of the output transducer 114 thereon.

The principles of operation shown in FIG. 15 can be extended to a curvedsurface, as shown in the embodiments of FIGS. 17 and 17A. In FIG. 17,for example, a pair of hemispherical shells 125 and 126 are used to forma spherical outer shell concentrically mounted with reference to aninner sphere 127, the latter being in effect a stabilized sphericalplatform as discussed with reference to FIG. 10. Three input transducerelements 128 are positioned on the outer surface of hemispherical shell125 at known points, or regions, A, B and C, respectively. Six receivertransducers, shown as transducer pairs 129, 130 and 131, are placed onthe outer surface of inner sphere 127 adjacent the inner surface ofshells 125 and 126. The six receiver transducers are positioned in pairsat the end points of three mutually orthogonal axes passing through thecenter of sphere 127, as shown (only one of the transducers of pair 131can be seen in the figure). The input transducers 128 are driven by asuitable multiplexed signal source so as to produce omnidirectionalacoustic travelling wave signals in hemispherical shell 125 successivelyemanating from each of the input transducers which signals are receivedby those of the receiver transducers which are adjacent the innersurface of shell 125. The input transducers may be of the form shown inFIGS. 16 and 16A and the receiver transducers may be of the typediscussed above with reference to FIG. 15. Appropriate triangulationtechniques are used to provide a measurement of the position of theinner sphere 127 relative to the outer sphere formed by hemisphericalshells 125 and 126 via a suitable position computation means whichcompares the received signals picked up by those of the receivertransducers 129, 130 and 131 which have detected the presence of theacoustic wave signal on hemispherical shell 125 with the transmittedsignals from the multiplexed signal source. A suitable damping material132, such as clamped rubber, may be placed around the periphery ofhemispherical shell 125 to prevent reflections of the acoustic wavesignals at the discontinuity formed thereby.

An alternative embodiment of the configuration shown in FIG. 17 is shownin FIG. 17A wherein a pair of hemispherical shells 160 and 161 enclosean inner sphere 162, as before. Three input transducers 163 are placedat arbitrarily selected but known positions on the outer surface ofshell 160 and three input transducers 164 are placed at arbitrarilyselected but known positions on the outer surface of shell 161, asshown. Three receiver transducers 165 are placed at known positions onthe outer surface of inner sphere 162 adjacent the inner surfaces ofshells 160 and 161. The position of receiver transducers 165 areselected so that they do not all lie on a common plane which passesthrough any great circle of sphere 162. The input transducers are drivenby an appropriate multiplexed signal source so as to produceomnidirectional acoustic travelling wave signals in hemispherical shells160 and 161 emanating successively from each of the input transducers.The presence of such signals are appropriately detected by the receivertransducers 165. Suitable triangulation techniques are used by anappropriate position computation means to provide a measurement of theposition of inner sphere 162 relative to the outer spherical shellformed by shells 160 and 161 by suitable comparisons of the receivertransducer signals with the transmitted signals from the multiplexedsignal source. As above, suitable damping materials 166 and 167 areplaced on each of the peripheries of shells 160 and 161.

In many applications the embodiment of FIG. 17 may be preferred to thatof FIG. 17A since in the former embodiment only a single hemisphericalshell (shell 125) need be precisely made and aligned with inner sphere127 and only a single damping strip need be used at the discontinuityregion.

The replacement of line, or bend, delay line elements with planar, orcurved, surface delay elements provides advantages in some applications.In the configuration of FIGS. 17 and 17A, for example, the heat transferfrom the inner sphere to the outer shells tends to be improved incomparison to the heat transfer capability of a band type configurationsuch as shown in FIG. 10. Moreover, a reduction in the electroniccomponents normally required to be mounted within the inner sphere inthe latter configuration can be achieved. Further, the assembly anddisassembly of the apparatus for maintenance and repair purposes, aswell as the mounting of the overall structure during use is simplified.Since the hemispherical shells of the type required in FIGS. 17 and 17Aare used in presently known systems and are, therefore, generallyavailable, they can be used in such configurations without the need fordesigning new components. Accordingly, the overall costs of manufactureare reduced.

Many of the discontinuity problems, particularly with regard to magneticbias problems at discontinuity points, and other interface problems atcross-over and termination points of the configuration of FIG. 10 areeffectively eliminated by the configurations of FIGS. 17 and 17A.Moreover, the signal to noise ratio should also be improved. Anadditional advantage of the structure of FIGS. 17 and 17A is that theinput and output transducers can be positioned in such a manner that thetime delay measurements provide direct readout information, i.e.,information directly corresponding to the angles being measured, so thatthe data processing required to attain the desired attitude informationis greatly simplified.

In using the delay elements of the invention, particularly the delayline elements of the rod or band type as shown in various embodimentsdiscussed above, variations in temperature may produce errors in themeasurements involved due to changes in the phase propagation velocityof the acoustic wave which travels along the line as well as to changesin the length of the line as a function of temperature changes. Errorsdue to length variations are of less significance than phase velocityerrors and the length changes can be relatively easily compensated forby mounting the delay line in a nonrigid manner at its ends so thatincreases in length do not vary the "active" length of the delay line,so that the direction of the delay line does not change, and, hence, thecharacteristics of the acoustic travelling wave signal do not change asthe delay line expands or contracts.

Phase velocity errors can be compensated, for example, in the delay lineconfiguration having input and output transducers 121 and 122 as shownin FIG. 18 by utilizing a reference transducer 123, such as a referencepickup coil, coupled to the delay line 120 at a fixed distance from theinput transducer 121. A comparison is made of the difference between thephase of the reference picked up signal at transducer 123 and the phaseof the input signal in a phase-locked loop circuit which changes thefrequency of the input signal effectively to reduce said phasedifference to zero. Any convenient phase-locked loop circuit known tothe art can be used. In this way, even in view of temperaturevariations, the phase velocity can be maintained substantially constantby appropriately controlling the frequency of the input signal.

While in the embodiments discussed above normally the input or drivertransducer is shown at a fixed reference position and the receivertransducer moved with respect thereto, the functions of the input andreceiver transducers may be effectively interchanged. Thus, in someapplications, the receiver transducer may be maintained at a fixedreference point and the input, or driver, transducer, or transducers,moved with respect thereto so that the relative distance, or distances,therebetween can be measured in substantially the same manner. Further,while the means for providing a magnetic bias for the magneticallycoupled delay elements discussed in the various embodiments of theinvention described above are not specifically shown, it is clear thatmany suitable means for providing such magnetic bias are well known tothose in the art and, accordingly, need not be depicted in detail here.

In describing the embodiments of the devices discussed above, the wavewhich is caused to travel along the delay element is not necessarilylimited to any specific type thereof. In the broader sense then suchdevices can utilize waves propagated in longitudinal, torsional, ortransverse modes. Since it is desirable, however, in most applicationsto achieve as high a spatial resolution as possible of the measurementwhich is to be made, it is preferable to select the most effective modeof propagation which can achieve such high resolution.

It is found that the most effective manner of achieving high resolutionlies in the use of a transverse mode of wave propagation in the delayelement, as opposed to either longitudinal or torsional modes thereof.Both longitudinal and torsional modes are virtually non-dispersive innature and have different velocities of propagation. The longitudinalvelocity V_(L) can be expressed as:

    V.sub.L = √E/ρ

and the torsional velocity V_(TO) as

    V.sub.TO = √μ/ρ

where E is Young's Modulus of the propagation medium, ρ is the densityof the medium, and μ is the rigidity modulus of the medium. For a nickelmagnetostrictive medium, for example, the longitudinal velocity V_(L) is4900 meters/second and the torsional velocity V_(TO) is 2950meters/second.

Thus, the torsional mode of vibration gives approximately 1.6 times thedelay per unit length as the longitudinal mode of vibration, which wouldgenerally mean an increased spatial resolution of about 1.6 of that ofthe longitudinal mode. However, the torsional mode has a lowelectromechanical coupling coefficient and, in general, requiresrelatively complex transducers so that, despite its increasedresolution, it is more difficult to implement and in many applicationsthe longitudinal mode would be preferred thereover.

In many other applications, however, a preferred embodiment of theinvention would utilize the transverse mode of operation so as toprovide an even greater increase in resolution over the longitudinal andthe torsional modes. Such increased resolution occurs because thetransverse mode creates a greater effective time delay per unit, i.e., alower velocity of propagation, than either the longitudinal or torsionalmodes. Unlike the longitudinal and torsional modes, the transversevelocity of propagation is dispersive in character and its nature isdependent upon the frequency f of the signal being propagated and on thephysical dimensions of the delay line medium. Thus, the transverse phasevelocity V_(TR) of each frequency component of a transversely vibratingstrip of medium can be expressed as:

    V.sub.TR = √ω V.sub.L K

where ω= 2πf, V_(L) is the longitudinal phase velocity, and K is theradius of gyration of the cross sectional area of the medium, K beingequal to d/√12 for a delay element in the form of a strip having athickness d.

An embodiment of the invention showing the use of transverse waves inthe delay element is shown in FIG. 22. As seen therein, a thin strip 176of magnetostrictive material, such as nickel, has a first transversemode driver transducer 175 comprising, for example, a pair of U-shapedelectromagnets positioned opposite the flat surface of strip 176. Atransverse mode receiver transducer 177 having essentially the sameconfiguration as that of the driver transducer 175 is positioned alongsaid magnetostrictive medium at a position to be determined. The delayelement 176 has vibration-damping termination means 184 at each endthereof. The coils associated with driver transducer 175 may be suppliedwith an excitation signal from an appropriate signal source as discussedin more detail below.

The receiver transducer 177 picks up the transverse wave which ispropagated along delay element 176 and supplied such pickup signal to asuitable phase detection system for use in determining the coarse andfine read-out position thereof as also discussed below in more detail.

The ratio of the longitudinal velocity to the transverse velocity V_(L)/V_(TR) for a nickel strip such as shown in FIG. 2 having a thickness of0.48 mm. can be calculated at different frequencies to show the ratio oftime delays per unit length, such time delays for a transverse modebeing thereby compared to those for a longitudinal mode. Thus, at 10 KHzone can obtain approximately 24 times more time delay per unit length ofthe delay element by utilizing the transverse mode of operation asopposed to a longitudinal mode of operation which provides a consequentincrease in resolution. Such resolution can be improved even further to48 times more delay per unit length if the thickness of the nickel stripis decreased from 0.48 mm. to 0.12 mm. Theoretical values of otherratios of V_(L) to V_(TR) at different frequencies are shown in thetable below.

    ______________________________________                                        (KHz)   1    10    50   100  200  400  800  1000 5000                         V.sub.L /V.sub.TR                                                                    75    24    10.6 7.5  5.3  3.74 2.65 2.37 1.06                         ______________________________________                                    

Since the transverse velocity of propagation V_(TR) varies as the squareroot of the longitudinal velocity of propagation V_(L), the use of atransverse mode makes the overall system less sensitive to temperaturevariations, residual stresses, and impurities in the material.

The use of such a transverse mode of vibration in a thin strip ofmagnetostrictive material can be applied to essentially all of theembodiments of the invention described herein in order to increase theresolution of such embodiments at different frequencies over what isattained when such embodiments utilize only longitudinal modes ofvibration. In determining coarse and fine readout data, however, becauseof the dispersive nature of transverse elastic waves, the use of anamplitude modulated wave and the signal processing system discussed withreference to FIG. 1 is not appropriate. Such a dispersive transversewave would tend to "smear" as it travelled along the delay element,thereby making it substantially impossible to detect the presence of thetransverse wave at the receiver transducer in order to operate the timedelay counter thereof.

One suitable technique for providing coarse and fine readout informationusing transverse waves is shown in FIG. 22. In the system shown therein,a transverse wave of a first frequency is sinusoidally modulated with asignal having a second, lower frequency. Thus, a voltage-controlledamplitude signal generator 169 is supplied with a sinusoidal modulatingsignal from a signal generator 170. The carrier frequency of themodulated signal from signal generator 169 may have, for example, arelatively high frequency, such as 269.680 KHz., while the modulatingsignal from signal generator 170 has a lower frequency, for example,such as 5.468 KHz.

The modulated signal is supplied to driver transducer 175 and to a phasedetector circuit 171. The signal received at receiver transducer 177 issuitably amplified by amplifier 172, the output of which is alsosupplied to phase detector 171. The amplifier output is also supplied toa linear envelope detector circuit 173 to obtain the envelope, ormodulating, signal which is thereupon supplied to a phase detectorcircuit 174. The other input to phase detector 174 is supplied fromsignal generator 170. Accordingly, the phase comparison of thetransmitted and received lower frequency signal at phase detector 174produces the coarse readout information and the phase comparison of thetransmitted and received higher frequency signal at phase detector 171produces the fine readout information, as required. Appropriatesynchronization of the operation of signal generator 170 with that ofsignal generator 169 can be provided by a suitable synchronizing signalfrom generator 169 to generator 170 as would be well known to those inthe art.

While the system disclosed in FIG. 22 utilizes a sinusoidally modulateddriver excitation signal in order to detect coarse and fine readout, insome applications it might be more advantageous to detect coarse readoutby utilizing either a longitudinal or torsional mode wave while at thesame time utilizing the transverse mode wave in combination therewith toproduce the fine readout data. Such a system is shown in FIG. 23. Asseen therein, a first driver transducer 175 provides a transverse modeof vibration of a travelling wave on delay element 176 which is pickedup by receiver transducer 177 in substantially the same manner asdiscussed with reference to FIG. 22. The delay element 176 hasappropriate vibration damping termination means 184 at each end, asshown. A further driver transduer 178 provides a travelling wave whichvibrates in a longitudinal mode along delay element 176 which wave ispicked up by a second receiver transducer 179. The driver and receivertransducers 178 and 179, respectively, for the longitudinal vibratingmode may be, for example, in the form of coils encircling the delayelement 176 as shown. A continuous wave signal from CW signal souce 180is supplied, for example, at different times to the transverse modedriver transducer 175 and to the longitudinal mode driver transducer 178via suitable switching circuitry 184. When the signal is supplied todriver transducer 178 the longitudinal travelling wave signal therebyproduced on delay element 176 is picked up by receiver transducer 179and supplied via a suitable switching circuit 185 operated incoordination with switch 184 to amplifier 182. The output of amplifier182 is in turn supplied to phase detector circuit 183 for comparisonwith the signal from CW signal source 180 to produce the coarse readoutinformation.

When the switching circuits 184 and 185 are such as to be connected tothe transverse mode transducers 175 and 177, respectively, thetransverse wave which is produced on and picked up from delay element176 is similarly processed by phase detector 183 to produce the finereadout information. Thus, in this operation each of the receivertransducers 177 and 179 picks up the desired traveling wave of itsrespective transverse or longitudinal mode signal and does not pick upthe traveling wave of the other mode.

Alternatively, signals of different frequencies may be suppliedsimultaneously to transducers 175 and 178, respectively, in order toavoid the need for the switching operation of FIG. 22. In such caseseparate signal sources and amplifier/phase detector circuitry arerequired for the coarse and fine readout operations.

Although the embodiments shown in FIG. 22, for example, depict a singlereceiver transducer 177, in some applications in order to achieveadvantages of averaging the phase measurements involved, a plurality oftransverse mode receiver transducers spaced at half wave lengthintervals along the delay element can be utilized as shown in FIG. 24.As seen therein, the receiver transducers are spaced from each other bya distance equal to the wave length of the travelling wave. The outputsthereof are summed serially by connecting the outputs of each of thetransducers together as shown and provide a desired output signal inwhich the accuracy of the phase measurement thereof is enhanced sinceany discrepancies therebetween are, in effect, averaged out. The outputsignal is used in the same manner in which the output signal from asingle receiver transducer is utilized in order to determine the finereadout data.

In the embodiments of FIGS. 19-21, for example, and in FIGS. 15 and 17,for example, the dimensions of the transducers are selected tocorrespond to a certain wavelength at a given frequency for thelongitudinal mode. Since c=fλ holds for any mode of vibration, it ispossible to use the same transducer to create transverse modes havingthe same wavelength at a different and specific frequency. Therefore,the transverse mode can be generated in such embodiments.

As discussed with respect to the embodiments of FIGS. 4 and 5 hereinsine and cosine signals can be obtained from the system of theinvention. An alternative method therefor is shown in FIG. 25 whichutilizes a configuration for creating a standing wave in the delayelement having two receiver transducers spaced apart by a distance "d"equal to ##EQU1## where λ is the wavelength of the driver excitationsignal and n is an integer. Thus a delay element 190 has a stationarydriver transducer 191 and a pair of receiver transducers 192 and 193which move together along delay element 190 and are positioned with theabove designated spacing from each other (alternatively the receivertransducers may be stationary and the driver transducer moved along thedelay element 190).

In the embodiment of FIG. 25 the delay element 190 does not include anyvibration damping termination means at either end. Consequently, whenthe driver transducer is excited, a standing wave is created in thedelay element. The outputs of the receiver transducers are inquadrature, i.e., the output of the receiver transducer 192 represents asine output signal while that of transducer 193 represents a cosineoutput signal.

A further alternative embodiment of the sine-cosine signal generatorwhich provides such trigonometric functions for a rotating shaft angle θis shown diagrammatically in FIG. 26. In this case the delay element 195is circular in shape and is positioned so as to rotate with a rotatingshaft 199 at an angular velocity ω. A pair of receiver elements 196 and197, spaced as discussed above, are positioned at one end thereof. Thedelay element 195 has no termination means at either end so that astanding wave is created therein by driver transducer 198 which, in thiscase, is a square wave loop pattern transducer which surrounds the delayelement 195 and is mounted stationary with respect to the rotatingshaft. Alternatively the configuration may be arranged so that thedriver transducer rotates with rotating shaft 199 while the delayelement remains stationary. The outputs from receiver transducers 196and 197 produce signals representing the sine and cosine of the angle θbetween the driver excitation input and receiver transducer positions.Such a system may be useful, for example, in obtaining sine and cosinedata from gimbal angle readouts in a gimbal system. The sine and cosineoutputs from the receiver transducers can be processed by conventionalresolver circuits.

Other variations in the particular structures of the transducers ormodifications of the configurations discussed in the various embodimentsof the invention may occur to those in the art within the spirit andscope of the invention. Hence, the invention is not to be construed aslimited to one or more of the particular embodiments shown and describedherein except as defined by the appended claims.

What is claimed is:
 1. A position determining apparatus comprising atleast one delay element having magnetic properties and capable ofestablishing electromagnetic fields associated with travellingcontinuous elastic wave signals in the delay element;at least one drivertransducer means coupled to said delay element at a reference positionand capable of producing transverse elastic wave signals in said delayelement; means for activating said at least one driver transducer meansto produce electromagnetic fields associated with at least onecontinuous transverse elastic wave signal which travels in said delayelement; at least one receiver transducer means coupled to said delayelement at said position to be determined relative to said referenceposition, said at least one receiver transducer means detecting thepresence of electromagnetic fields associated with said travellingcontinuous transverse elastic wave signal as it travels past saidposition to produce a detected continuous transverse wave signal; meansresponsive to said detected continuous wave signal and to said activatedcontinuous wave input signal for determining the position of said atleast one receiver transducer relative to said reference position, saidposition determining means includingmeans for comparing the phase ofsaid detected continuous transverse wave signal as detected at saidposition to be determined with the phase of said activated continuoustransverse wave input signal at said reference position; and means forsubstantially reducing reflections of travelling elastic waves in saiddelay element.
 2. A position determining apparatus comprising at leastone nonfluid delay line element having magnetic properties and capableof establishing electromagnetic fields associated with unidirectionalelastic wave signals in the delay line element, said delay line elementforming a specified curved path;a first reference point having apreselected spatial relationship with said curved path; at least onedriver transducer means coupled to said delay line element at areference position which forms a reference line with said firstreference point; means for activating said at least one drivertransducer means to electromagnetic fields associated with at least onetransverse elastic wave signal which travels in said delay line element;at least one receiver transducer means coupled to said delay element ata second position, the line between said second position and saidreference forming an angular position to be determined with respect tosaid reference line, said at least one receiver transducer meansdetecting the presence of said electromagnetic fields associated withsaid travelling transverse elastic wave as it travels past said secondposition to produce a detected signal; and means responsive to saiddetected signal and to said activated signal for determining saidangular position relative to said reference line.
 3. A positiondetermining apparatus comprisingat least one first delay line elementcapable of supporting a first travelling elastic wave signal in adirection along a first specified path; at least one first transducermeans coupled to said delay line element at a first position; meanscapable of activating said at least one transducer means to produce atleast one transverse elastic wave signal which travels in said at leastone first delay line element; at least one second delay line elementcapable of supporting a second travelling transverse elastic wave signalin a direction along a second specified path different from said firstspecified path and coupled to said at least one first delay line elementat a common position, said at least one first delay line element andsaid at least one second delay line element each capable of detectingthe presence of a travelling signal in the other delay line elements asit travels past said second position; at least one second transducermeans coupled to said at least one other delay line element at a secondposition; means capable of activating said at least one secondtransducer means to produce at least one transverse elastic wave signalwhich travels along said at least one other delay line element; each ofsaid delay line elements being capable of detecting the presence at saidcommon position of a transverse elastic wave signal travelling along theother of said delay lines; and each of said delay line elementsincluding means responsive to the detected signal in the other delayline element to its own activated signal for determining said first andsecond positions relative to said common position.
 4. An apparatus fordetermining a position on a curved surface comprisingthree mutuallyorthogonal delay lines each being capable of establishingelectromagnetic fields associated with travelling elastic wave signalsand forming three mutually orthogonal and specified curved paths on saidcurved surface; each of said delay lines having a transducer located ata reference point on the curved path formed by each of said delay linesfor activating a travelling transverse elastic wave signal on each ofsaid delay lines; a fourth delay line forming a curved path having anangular relationship with each of the three mutually orthogonal curvedpaths formed by said three mutually orthogonal delay lines, said fourthdelay line being capable of detecting the presence of a travellingtransverse elastic wave signal on each of said delay lines; and meansresponsive to said detected waves for measuring the angularrelationships between said fourth delay line and each of said threemutually orthogonal delay lines whereby said position on said curvedsurface is determined.
 5. A position determining apparatus comprising adelay element capable of supporting a travelling continuous elastic wavesignal;a first transducer coupled to said delay element at a firstregion thereof for activating a first continuous transverse elastic wavesignal having a specified wavelength, λ, along said delay element; asecond transducer coupled to said delay element at a second regionthereof at a distance from said first transducer equal to (λ/4 + N2π),where N is 0 or an integer, for activating a second continuoustransverse elastic wave signal having said specified wavelength, λ,along said delay element; receiver transducer means coupled to saidelement at said second region corresponding to said position to bedetermined for detecting the presence of said continuous transverseelastic wave signals as they travel past said position; means responsiveto said detected signals to obtain amplitude modulated sine and cosinesignals for determining said position; and means for substantiallyreducing reflections of said travelling continuous elastic wave signalsin said delay element.
 6. A position determining apparatus comprisingasaid element capable of supporting a travelling continuous elastic wavesignal; a transducer coupled to said delay element at a first regionthereof for activating a continuous transverse elastic wave signalhaving a specified wavelength, λ, along said delay element; a firstreceiver transducer coupled to said delay element at a first position; asecond receiver transducer coupled to said delay element at a secondposition at a distance from said first receiver transducer equal to(λ/4+ N2π) where N is zero or an integer, each of said receivertransducers detecting the presence of said travelling transverse elasticwave signal as it travels past said first and second positions; meansresponsive to said detected signals to obtain amplitude modulated sineand cosine signals for determining said position; and means forsubstantially reducing reflections of said travelling continuoustransverse elastic wave signals in said continuous elastic wave signalsin said delay element.
 7. A position determining apparatus comprisingatleast one nonfluid delay element having magnetic properties and capableof establishing electromagnetic fields associated with omnidirectionaltravelling elastic wave signals in the delay element; at least onetransducer means electromagnetically coupled to said delay element at atleast one reference position; means for activating said at least onetransducer means to produce electromagnetic fields associated with atleast one transverse elastic wave signal which travels in said delayelement omnidirectionally from said at least one reference position; atleast one other transducer means coupled to said delay element at saidposition to be determined relative to said reference position, said atleast one other transducer means detecting the presence of saidtravelling transverse elastic wave signal as it travels past saidposition; means responsive to said detected signal and to said activatedsignal for determining the position of said at least one othertransducer relative to said reference position.
 8. A positiondetermining apparatus comprisinga delay element having magneticproperties and a planar surface and being capable of establishingelectromagnetic fields associated with an omnidirectional travellingelastic wave signal; at least one transducer means comprising at leasttwo transducers coupled to and located at known positions on said planarsurface with respect to each other; means for establishingelectromagnetic fields by activating at least two omnidirectionaltransverse elastic wave signals in said planar surface travelling fromsaid known positions; at least one other transducer means comprising areceiver transducer electromagnetically coupled to and located at aposition to be determined relative to said known positions andresponsive to said at least two transverse elastic wave signals fordetecting the presence of said electromagnetic signals as they travelpast said position to be determined; and means responsive to saidelectromagnetic fields associated with activated elastic wave signalsand said detected electromagnetic signals for determining said position.9. An apparatus in accordance with claim 7 wherein said nonfluid delayelement is a first solid spherical surface; said at least one transducermeans comprises at least two transducer means located at known positionson said spherical surface with respect to each other for activating atleast two omnidirectional transverse elastic wave signals in saidspherical surface travelling from said known positions;said at least oneother transducer means comprises a receiver transducerelectromagnetically coupled and located on a second spherical surfaceconcentric with said first spherical surface at a position to bedetermined relative to the known positions of said at least twotransducer means and responsive to said at least two signals fordetecting the presence of said transverse signals as they travel pastsaid position to be determined; and means responsive to said activatedtransverse elastic wave signals and said detected electromagnetic fieldsassociated with said transverse elastic wave signals for determiningsaid position.
 10. A position determining apparatus comprisinga delayelement capable of supporting a travelling elastic wave signal andmounted on a first member; an input transducer coupled to said delayelement for activating a continuous transverse elastic wave signal whichtravels along said delay element; an output transducer comprising aplurality of receiver transducer elements coupled to each other and tosaid delay element for detecting the presence of said travellingtransverse elastic wave signal on said delay element, said transducerelements being spaced by distances equal to multiples of half wavelengthof said travelling continuous elastic wave signal over at least a regionof said delay element, and said receiver transducer elements beingmounted on a second member adjacent said first member; means responsiveto said detected continuous transverse elastic wave signals fordetermining the position of said receiver transducer elements relativeto a reference region on said delay element; and means for substantiallyreducing reflections of said travelling continuous transverse elasticwave signals in said delay element; said first and second members beingrelatively movable with respect to each other.
 11. A system inaccordance with claim 1 wherein said at least one receiver transducermeans positioned at said position to be determined includes a pluralityof receiver transducer means spaced apart from each other by a distanceequal to an integral number of wavelengths of said continuous transverseelastic wave signal.
 12. A system in accordance with claim 1 whereinsaidactivating means activates said at least one driver transducer means toproduce a transverse travelling elastic wave on said delay elementcomprising a first carrier signal having a first frequency modulated bya second modulating signal having a second frequency lower than saidfirst frequency; said position determining means includinga first phasecomparison means for comparing the phase of said carrier signal detectedat said position to be determined and the phase of said activatedcarrier signal at said reference position; and second phase comparisonmeans for comparing the phase of said modulating signal detected at saidposition to be determined and the phase of said activated modulatingsignal at said reference position.
 13. A system in accordance with claim12 wherein said modulating signal is a sinusoidal signal.
 14. A systemin accordance with claim 1 and further includingat least one furtherdriver transducer means coupled to said delay element at said referenceposition and capable of producing non-transverse elastic wave signals insaid delay element; means for activating said at least one furthertransducer means to produce electromagnetic fields associated with atleast one continuous non-transverse elastic wave signal which travels insaid delay element; at least one further receiver transducer meanscoupled to said delay element at said position to be determined fordetecting the presence of electromagnetic fields associated with saidtravelling continuous non-transverse elastic wave signal as it travelspast said position to produce a detected continuous non-transverse wavesignal; and further wherein said position determining meansincludesmeans for determining the position of said further at least onereceiver transducer means; and means for comparing the phase of saiddetected non-transverse wave signal with the phase of said activatednon-transverse wave input signal to determine the position of saidfurther at least one receiver transducer means.
 15. A system inaccordance with claim 14 wherein said at least one driver transducermeans which produces transverse elastic wave signals and said further atleast one driver transducer means which produces non-transverse elasticwave signals are activated at different times.
 16. A positiondetermining device comprisinga delay element capable of supporting atravelling continuous elastic wave signal and further capable ofproviding a standing wave signal therein; a transducer coupled to saiddelay element at a first region thereof for activating a continuouselastic wave signal having a specified wavelength, λ, along said delayelement, said delay element having reflective ends for producing astanding wave of said wavelength therein; a first receiver transducercoupled to said delay element at a first position; a second receivertransducer coupled to said delay element at a second position at adistance from said first receiver transducer equal to λ(1+2n)/4 where nis zero or an integer, each of said receiver transducers detecting thepresence of said standing wave signal at said first and secondpositions; and means responsive to said each of detected signals forproviding amplitude modulated sine and cosine signals, respectively fordetermining said position.
 17. A position determining apparatuscomprisinga delay element capable of supporting a travelling elasticwave signal, said delay line element having a substantially circularconfiguration, said delay elememt having reflective ends and beingcapable of producing a standing wave therein; an input transducercomprising a plurality of transducer elements coupled to each other andto said delay element for activating a continuous elastic wave signalhaving a specified wavelength λ which travels along said delay elementand produces a standing wave signal of said wavelength therein, saidtransducer elements being spaced by distances equal to multiples of halfwavelength of said travelling continuous elastic wave signal over atleast a region of said delay element, said input transducer having asubstantially circular configuration and being mounted substantiallyconcentrically with and adjacent said delay line element; a firstreceiver transducer coupled to said delay element at a first position; asecond receiver transducer coupled to said delay element at a secondposition at a distance from said first receiver transducer equal toλ(1+2n)/4 where n is zero or an integer, each of said receivertransducers detecting the presence of said standing wave signal at saidfirst and second positions; said delay element and said input transducerbeing relatively movable with respect to each other; and meansresponsive to each of said detected signals for providing amplitudemodulated signals representing the sine and cosine functions of theangular position of said delay element and said input transducerrelative to each other.